Papers › Accelerating BAO Scale Fitting Using Taylor Series

Accelerating BAO Scale Fitting Using Taylor Series

13 Dec 2021arXiv:2112.06438links table onlyarchive 2025-07-28

Matthew Hansen, Alex Krolewski, Zachary Slepian

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The Universe is currently undergoing accelerated expansion driven by dark energy. Dark energy's essential nature remains mysterious: one means of revealing it is by measuring the Universe's size at different redshifts. This may be done using the Baryon Acoustic Oscillation (BAO) feature, a standard ruler in the galaxy 2-Point Correlation Function (2PCF). In order to measure the distance scale, one dilates and contracts a template for the 2PCF in a fiducial cosmology, using a scaling factor α. The standard method for finding the best-fit α is to compute the likelihood over a grid of roughly 100 values of it. This approach is slow; in this work, we propose a significantly faster way. Our method writes the 2PCF as a polynomial in α by Taylor-expanding it about α= 1, exploiting that we know the fiducial cosmology sufficiently well that α is within a few percent of unity. The likelihood resulting from this expansion may then be analytically solved for the best-fit α. Our method is 48-85× faster than a directly comparable approach in which we numerically minimize α, and $\sim$$12,000 \times$ faster than the standard iterative method. Our work will be highly enabling for upcoming large-scale structure redshift surveys such as that by Dark Energy Spectroscopic Instrument (DESI).

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